Patent GB-652763-A (GB)
Title: Improvements in or relating to means for producing currents of audio frequency
IPC: H02P5/50
Filed: 1948-04-09
Abstract: 652,763. Automatic control systems for motor-alternators. COMPAGNIE POUR LA FABRICATION DES COMPTEURS ET MATERIEL D'USINES A GAZ. April 9, 1948, No. 9993. Convention date, April 9, 1947. [Class 38 (iv)] Electric motor-driven alternators operating in parallel and producing audio-frequency to be superimposed on electrical distribution networks, have their speed and the division of load between them automatically adjusted to predetermined values. In Fig. 1 shunt motors 2, 9 supplied from a D.C. source 1 drive alternators 5, 12 which are paralleled by closing a switch 16 when a voltmeter 17 supplied by the opposed outputs of tachometer alternators 8, 15 indicates zero, the tachometer alternators being so designed that the main alternators are then running at the same speed and are in phase. Voltmeter 17 may be replaced by a no-volt time delay relay which energizes a winding 161 to operate switch 16 automatically. Upon deviation of the speed of the main alternators from a predetermined value, corresponding variation of the frequency of tachometer alternator 8 is detected by a frequency-responsive relay 21 which, through contact 22 or 23 and relays 24, 26 or relays 25, 27, causes reversible servomotor-operated rheostats 19 and 20 to run in the appropriate direction to adjust the speeds of both motors 2, 9 by field control. If, however, there is unbalance of the load currents of motors 2, 9 it is detected by a differential relay 29, energized from shunts 32, 33, which, through contact 291 or 29<SP>11</SP> and relay 34 or relay 35 renders one servomotor-operated rheostat only operable to increase speed and the other only operable to decrease speed so that speed corrections also lead to equalization of load. The field windings of alternators 5, 12 are supplied from source 1 through a servomotor-operated rheostat 18 for voltage adjustment. Parallel operation of more than two main alternators with differential relays comparing the current of each motor with the sum of motor currents is referred to. Relay 29 may be designed to maintain the load ratio at a value other than unity in which case two voltage controlling rheostats operated in tandem replace rheostat 18. In a modification, Fig. 2 (not shown), the motor field windings are energized from separate amplidyne exciters each having three control windings. Each control winding of one exciter is connected in series or parallel with a control winding of the other exciter. One pair of control windings influence the exciters in the same sense and are energized from a D.C. source through a datum setting rheostat. A second pair influence the exciters in opposite senses and are energized by the differential voltage from shunts, corresponding to shunts 32, 33 in Fig. 1, to maintain a predetermined load division. The third pair influence the exciters in the same sense and are energized by means giving a D.C. output, the magnitude and polarity of which is dependent on the magnitude and sense of frequency deviation of a tachometer alternator, corresponding to tachometer alternator 8 in Fig. 1, to maintain a predetermined speed. Parallel operation of more than two main alternators with this arrangement is also referred to.